eukaryotic translation machinery by kk sahu

Introduction
Components of protein synthesis
Translation in eukaryotes
1.initiation
2.elongation
3.Termination
Conclusion
references

1. eukaryotic translation machinery , By KAUSHAL KUMAR SAHU Assistant Professor (Ad Hoc) Department of Biotechnology Govt. Digvijay Autonomous P. G. College Raj-Nandgaon ( C. G. )

2. Synopsis: Introduction Components of protein synthesis Translation in eukaryotes 1.initiation 2.elongation 3.Termination Conclusion references

3. Introduction: Protein synthesis is the process in which cells build protein . Protein synthesis consist of two main events, transcription and translation.

4. Translation: The process by which protein is synthesized is called translation. because the language of nucleic acid base is translated into language of amino acid.

5. Protein biosynthesis The main components of protein biosynthesis are: Activation of Amino acid. Ribosome messenger RNA. Transfer RNA. Energy source & protein factor.

6. Ribosome Ribosome are the site for protein synthesis. Prokaryote- 70S & Eukaryote- 80S The ribosome has 2 site. (1)A site (2) P site. A site is for binding of the aminoacyl t RNA & P site is for binding of peptidyl t RNA. Eukaryotes contain A, P & E site. A-site is called= acceptor site , P is donor site & E is exit side.

7. Ribosome:

8. mRNA The specific information which are required for protein synthesis is present on mRNA. the DNA has passed on the genetic information in the form of codans to the mRNA to translate into a protein sequence.

9. tRNA It play the central role in translation. Amino acid is covalently bound to the tRNA at the 3`-end Each tRNA has 3 nucleotide base sequence ( anticodon ) which is responsible to recognize the codon (complimentary bases) of mRNA for protein synthesis.

10. Energy sources &protein factors both ATP &GTP required for the supply of energy in protein synthesis. The process of translation involve a number of protein factors . They are important for initiation, elongation & termination .

11. Amino acid activation Group of 3 nucleotide that specifies an amino acid is known as codon Amino acids are the monomers which are polymerized to produced protein. Aminoacyl –t RNA synthetase activate amino acids by covalently linking them to t RNA .

12. Translation in eukaryote It divided into 3 major stage: 1. Initiation. Elongation. Termination.

13. Initiation it involve 10 eukaryotic initiation factors( eIFs ) Initiation can be divided into 4 steps: 1.ribosomal dissociation. 2. formation of 43S preinitiation complex. 3. formation of 48S initiation complex. Formation of 80S initiation complex .

14. Ribosomal dissociation The 80S ribosome dissociates to form 40S &60S subunits. Then 2 initiating factors eIF-3& eIF-1 bind to the 40S subunit.& block its re association with 60S subunits. eIF-3 &eIF-1 called anti association factor. 80S 40s 60S

15. Formation of 43S initiating complex Met- tRNA &eIF-2 bound to GTP & attaches to 40S ribosomal subunit to form 43S preinitiation complex. EIF-3 & eIF-1A stabilizes this complex. Met- tRNA is involved to the binding of initiating codon AUG. Met- tRNA GTP 40s 43S

16. Formation of 48S initiation complex The binding of mRNA to the 43S preinitiation complex results in the formation of 48S initiation complex. In eukaryote recognition sequence of initiation codon is called as kozak consensus sequence. In prokaryote shine- dalgarno sequence. mRNA 43s 48S

17. Formation of 80S initiation complex 48S initiation complex binds to 60S ribosomal subunit to form 80S initiation complex. The binding involve the hydrolysis of GTP.in this step eIF-5 is involved.

18. Elongation It may be divided into 3 steps: 1binding of aminoacyl t-RNA to A site. 2peptide bond formation. 3Translocation.

19. Binding of aminoacyl tRNA to Asite The 80S initiation complex contain met- tRNA in the P-site & the A-site is free .then another aminoacyl t-RNA is placed in the A-site. Elongation factor-1 involve in this process &energy supply by GTP. When the aminoacyl t-RNA is placed in the A-site then EF-1&GTP are recycled to bring another aminoacyl t-RNA.

20. Peptide bond formation The enzyme peptydyl transferase catalyses the formation of peptide bond. There is no energy require for the Peptide bond formation because amino acid in the aminoacyl t-RNA is already activated. The growing peptide chain attach to the tRNA in A-site then peptide bond formation take place.

21. Translocation As the peptide bond formation occurs, the ribosome moves to the next codon of mRNA towards 3`end the process is called translocation. It require EF-2 & GTP. GTP gets hydrolyzed &supply energy to mRNA then EF1 &GTP complex recycles for translocation. After the process tRNA moves into E-site from where it leaves the ribosome .

22. Elongation process:

23. Termination Termination of the protein synthesis occurs of the 3 stop codon UAA, UGA, UAG .they enters to A- site of the ribosome. There are no t-RNA molecule that recognize the stop codons . A release factor protein bind to the A-site & cause hydrolysis. The completed polypeptide is release &ribosome separated into small subunits for the preparation of next round of protein synthesis.

24. Conclusion: It is the most essential process for the conversion of mRNA to protein without which no gene would be able to code any functional protein. it forms the basis of many cellular and metabolic processes. transcription is the initial level at which gene expression is controlled the translation of mRNA is also regulated in both prokaryotic and eukaryotic cells.

25. REFERENCE BOOK NAME EDITION WRITER Biochemistry 3 RD edition U .satyanarayana Cell & Molecular Biology 6 th edition Gerald Karp INTERNET TIME www.authorstream.com 8/03/2013 6:30pm